Hi,
Not sure from the picture if those knobs are original or not, but if original it would be the low part of the Tenax buttons as found on Mercedes 111/112 convertibles to fasten the "Verdeckpersenning" - soft top cover. I've seen a few pagodas with these buttons, and always believed it would be original, since I know for sure that the Tonneau cover was a factory option that could be ordered for the W111/W112 convertibles. I would be surprised if it was impossible for a customer to order a Tonneau cover for his pagoda.